Yeah but you don't have to only eat vegetables to feel full. Just eating "normal" food in the right/limited amounts feels fine (at least after the first few weeks).

Also I doubt that people trying to diet would just eat a few candys for lunch and try to live with that.

And surprisingly the full-feeling does actually correlate with the amount of calories you eat. If you eat 2 strips of bacon (which doesn't seem much) and let it sit for some time (without eating more) hunger passes. Maybe not as much as with better food, but it still does to some degree.